Traditionally, food service equipment, tableware, serving utensils and other reusable food service items have been cleaned with solutions of alkaline detergents in a spray washing type machine, typically a dish washing machine or a pan washing machine. The cleaning operation is fairly straightforward and requires adequate water temperature and pressure, in combination with alkaline builders and other detergent ingredients to effectively emulsify the greases and oils and loosen and suspend the soils that are present and to allow them to be freely rinsed away from the tableware with a final rinse.
Presently available solid cast alkaline detergent compositions provide a uniform formulation throughout the life of the product (see for example those disclosed in U.S. Pat. Nos. RE32,818 and 32,763). However, providing a constant concentration of all formulation components can provide significant disadvantages.
Aside from mechanical operating conditions and limitations, including temperature, the greatest detriment to proper adequate cleaning and bright clean, spot-free, film-free results on the tableware has been water hardness. Other aspects of cleaning such as soil load, etc., are usually handled by increasing or varying the balance of alkaline components within the basic formulation. The results gained are not appreciably different with any alkaline component, be it an alkali metal hydroxide, an alkaline silicate or, for that matter in many cases, an alkaline phosphate or carbonate. The detrimental effects of hard water are handled in institutional and commercial warewashing and spray washing operations by either putting a water conditioning system in place before the cleaning operation or formulating the product to contain high levels of water conditioning agents. The most effective of these water conditioning agents are the complex phosphates which offer the benefits of synergistic enhancement of hard surface detergency and water softening.
However, the use of constant and sustained high levels of phosphates has significant disadvantages. For example, (1) high phosphate concentrations have a negative environmental impact; (2) high levels of complex phosphates are expensive components of a detergent formulation; and (3) the high level of phosphate required to effectively control or eliminate a lime/scale buildup are often high enough to unbalance the formula away from the effective cleaning material (i.e., the alkaline builder) toward the low alkalinity complex phosphate which is being used to control water hardness.
In practice, a commercial or institutional warewashing operation using hard water must periodically descale their washing machines with an acidic compound, which dissolves the lime/scale and restores the machine to its original bright finish. All acidic descalers have a corrosive effect on machine parts and/or plumbing. Unfortunately, this method does not eliminate film and buildup which may occur on the actual tableware and be highly noticeable on glass and crystal. To enhance results and offer film removal and reduced streaking on these types or surface, it is not unusual to use extremely high detergent concentrations to over condition the water or to use acidic or conditioning rinse aids which are substantially more costly than the ordinary sheeting agents used to accelerate the drying of tableware in machine washing operations. Furthermore, the washing equipment must be shut down during the deliming/descaling process, resulting in a loss of productive washing time.
It would, therefore, be desirable to provide a warewashing detergent composition that provided adequate detergency while also removing lime and scale from the washing equipment in which it is used. It would also be desirable to provides such a composition that would provide these deliming/descaling benefits without the need to shut down the washing equipment for the cleaning operation.
In many washing applications it may also be advantageous to provide varying degrees of active agents throughout the life of a detergent product. For example, it may be desirable to provide extra cleaning power at the end of product life before the detergent composition is changed in order to assure that alkalinity concentration is not depressed during the changeover process. It would therefore be desirable to provide detergent compositions which provided a heightened level of alkalinity as the product was used.
It may also be advantageous to periodically provide a strong dose of formulation components to provide other benefits. For example, use of high concentrations of silicates have been demonstrated to replenish glaze on the surface of china and other glazed table ware. It would therefore be desirable to provide detergent compositions in which the concentration of silicate is periodically increased to provide this replenishing effect.
It may also be advantageous to reduce the conductivity of the detergent solution produced by use of a solid cast alkaline detergent composition. Reducing the conductivity of late in the product life would cause the washing machine to increase the rate of dissolving the detergent composition, resulting in a higher concentration of active ingredient in the machine washing solution. It would therefore be desirable to provide a solid cast detergent product which would provide this type of variation in conductivity.
These and other advantages are provided by the present invention.